Semiconductor light-emitting element and method of manufacturing the same

ABSTRACT

There is disclosed a semiconductor light-emitting element comprising a substrate having a first surface and a second surface, a semiconductor laminate formed on the first surface of the substrate and containing a light-emitting layer and a current diffusion layer having a light-extracting surface. The light-emitting element is provided with a light-extracting surface which is constituted by a finely recessed/projected surface, 90% of which is constructed such that the height of the projected portion thereof having a cone-like configuration is 100 nm or more, and the width of the base of the projected portion is within the range of 10-500 nm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Applications No. 2002-010571, filed Jan. 18,2002, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor light-emitting elementsuch as a light-emitting diode (LED), a semiconductor laser (LD), etc.,and to a method of manufacturing the semiconductor light-emittingelement.

2. Description of the Related Art

A light-emitting diode of high luminance is conventionally constructedsuch that a light-emitting portion constituted by a double-heterostructure, etc., is disposed on the surface of a semiconductorsubstrate, and a current diffusion layer is deposited on thelight-emitting portion. As this light-emitting diode is packaged byresin, the upper portion of the current diffusion layer is covered witha transparent resin layer to protect the light-emitting element.

In the light-emitting diode constructed in this manner, the criticalangle between the current diffusion layer (refractive index 3.1-3.5) andthe layer of the transparent resin (refractive index about 1.5) iswithin the range of 25 to 29 degrees. Light having a larger incidenceangle than this critical angle is totally reflected, thus greatlydegrading the probability of the light being emitted from thelight-emitting element. Therefore, the extraction efficiency of thelight that can be actually generated from the light-emitting diode is aslow as 20% or so at present.

Incidentally, as for the method of roughening the surface of the currentdiffusion layer, there is known a technique of treating the surface ofthe current diffusion layer with hydrochloric acid, sulfuric acid,hydrogen peroxide or a mixed solution comprising these chemicals,thereby obtaining a surface-roughened chip (Japanese Patent UnexaminedPublication (Kokai) 2000-299494 and Japanese Patent UnexaminedPublication (Kokai) H4-354382). These methods are however accompanied bythe problem that due to the influence of the crystallinity of thesubstrate, the roughening of the surface of the current diffusion layermay become impossible depending on the orientation of the surface beingexposed. Therefore, roughening of the surface of the chip may notnecessarily be possible, so that, the extraction efficiency of the lightis prevented from being improved, thus making it difficult to enhancethe luminance of the light-emitting diode.

As described above, the conventional light-emitting diode packaged byresin is accompanied by the problem that the incident light to beentered obliquely into the interface between the uppermost layer of thesemiconductor multi-layer including a light-emitting layer and atransparent resin is totally reflect from the interface, thus degradingthe light extraction efficiency of the light. Further, this problem isnot limited to a light-emitting diode, but is also applicable to asurface-emitting type semiconductor laser.

BRIEF SUMMARY OF THE INVENTION

A semiconductor light-emitting element according to one embodiment ofthe present invention comprises:

-   -   a substrate having a first surface and a second surface; and    -   a semiconductor laminate formed on the first surface of the        substrate and containing a light-emitting layer and a current        diffusion layer;    -   wherein the light-emitting element is provided with a        light-extracting surface which is constituted by a finely        recessed/projected surface, 90% of which is constructed such        that the height of the projected portion thereof having a        cone-like configuration is 100 nm or more, and the width of the        base of the projected portion is within the range of 10-500 nm.

A method of manufacturing a semiconductor light-emitting elementaccording to one embodiment of the present invention comprises:

-   -   forming a semiconductor laminate on a first surface of a        substrate having a first surface and a second surface, the        semiconductor laminate containing a light-emitting layer and a        current diffusion layer;    -   determining a light-extracting surface for extracting light from        the light-emitting layer;    -   forming a polymer film comprising a diblock copolymer on the        light-extracting surface;    -   subjecting the polymer film to an annealing treatment, thereby        phase-separating the diblock copolymer into two phases;    -   eliminating one of the phases of the diblock copolymer that has        been phase-separated to form a mask material layer having a        pattern constituted by the other phase; and    -   transferring the pattern of the mask material layer to the        light-extracting surface to form finely recessed/projected        portions on the light-extracting surface.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a cross-sectional view illustrating the element structure ofan LED according to one embodiment of the present invention;

FIGS. 2A to 2D are cross-sectional views each illustrating the state offinely recessed/projected portions according to one embodiment of thepresent invention;

FIGS. 3A to 3D are cross-sectional views each illustrating, stepwise,the manufacturing steps of an LED according to one embodiment of thepresent invention;

FIGS. 4A to 4D are cross-sectional views each illustrating, stepwise,the manufacturing steps of an LED according to another embodiment of thepresent invention;

FIGS. 5A and 5B are cross-sectional views each illustrating the elementstructure of an LED according to a further embodiment of the presentinvention;

FIGS. 6A and 6B are cross-sectional views each illustrating the elementstructure of an LED according to a further embodiment of the presentinvention;

FIG. 7 is a cross-sectional view illustrating the element structure ofan LED according to a further embodiment of the present invention;

FIGS. 8A to 8C are cross-sectional views each illustrating, stepwise,the manufacturing steps of an LED according to a further embodiment ofthe present invention;

FIGS. 9A to 9C are cross-sectional views each illustrating, stepwise,the manufacturing steps of an LED according to a further embodiment ofthe present invention;

FIG. 10 is a microphotograph illustrating the features of therecessed/projected surface according to one embodiment of the presentinvention; and

FIGS. 11A to 11C are cross-sectional views each illustrating, stepwise,the manufacturing steps of an LED according to a further embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Next, the embodiments of the present invention will be explained indetail with reference to drawings.

First Embodiment

FIG. 1 is a cross-sectional view illustrating the element structure ofan LED according to a first embodiment of the present invention.

As shown in FIG. 1, on the top surface (the first surface) of an n-typeGaP substrate 10 are deposited semiconductor laminated layers comprisinga hetero structure portion 14 which is constituted by an n-type InAlPclad layer 11, an InGaAlP activated layer 12 and a p-type InAlP cladlayer 13; and a p-type GaP current diffusion layer 15. A p-sideelectrode (upper electrode) 16 is formed on part of the surface of thecurrent diffusion layer 15 with the remaining portion of the surface ofthe current diffusion layer 15 being left exposed. On the other hand, ann-side electrode (lower electrode) 17 is formed on the bottom surface(the second surface) of the substrate 10. The light emitted from theactivated layer 12 is taken up from the exposed surface of the currentdiffusion layer 15. Namely, the exposed surface of the current diffusionlayer 15 is employed as a light-extracting surface.

On this exposed surface of the current diffusion layer 15, there areformed finely recessed/projected portions 18. These finelyrecessed/projected portions 18 are formed by a diblock copolymer asexplained hereinafter, and configured as shown in FIG. 2A, for instance.In FIG. 2A, “h” is the height of the projected portion of therecessed/projected portions 18, while “d” is the length (width) of thebase of the projected portion.

This projected portion is triangular in cross section with the width ofthe base thereof (d) ranging from 10 to 500 nm, the height thereof (h)being 100 nm or more, and the apex angle thereof ranging from 25 to 80degrees, these numerical limitations being admitted as effective insecuring a sufficient effect to improve the light extraction efficiency.The non-uniformity in configuration of the projected portion within theelement was found, for example, 100±50 nm in width and 200±100 nm inheight (i.e. the distribution of width within the element: ±50%, and thedistribution of height within the element: ±50%).

At least part of the recessed/projected portions 18 may be constructedsuch that the tip end of the projected portion is provided with a finetransparent portion as shown in FIG. 2B. Alternatively, the tip end ofthe projected portion may be flattened as shown in FIG. 2C. Further, thetip end of the projected portion may be flattened and provided thereonwith a fine transparent portion as shown in FIG. 2D.

Next, the process of manufacturing the LED according to this embodimentwill be explained with reference to FIGS. 3A to 3D.

First of all, as shown in FIG. 3A, the hetero structure portion 14 andthe current diffusion layer 15 were successively epitaxially grown onthe top surface of the n-type GaP substrate 10. Then, the p-sideelectrode 16 was formed on a desired region of the surface of thecurrent diffusion layer 15, and the n-side electrode 17 was formed onthe bottom surface of the substrate 10.

Meanwhile, a 1:2.5 diblock copolymer comprising polystyrene (PS) andpoly(methyl methacrylate)(PMMA) was dissolved in a solvent formed ofethylcellosolve acetate (ECA) to prepare a solution of the copolymer. A1:2-3 diblock copolymer comprising PS and PMMA may be used, and it ispossible to use propylene glycol monomethyl ether acetate (PGMEA) orethyl lactate (EL) as a solvent.

This solution was then spin-coated over the current diffusion layer 15and the p-side electrode 16 at a rotational speed of 2500 rpm to form acoated film, which was then pre-baked at a temperature of 110° C. for 90seconds to volatilize the solvent to form a polymer layer 31 as shown inFIG. 3B. Thereafter, the polymer layer 31 was subjected to annealing ina nitrogen gas atmosphere at a temperature of 210° C. for 4 hours topermit the diblock copolymer to take place the phase separation thereofinto PS and PMMA.

The polymer layer containing this phase-separated diblock copolymer wasthen subjected to etching by RIE using CF₄ (30 sccm) under theconditions of 1.33 Pa in pressure and 100 W in power output. As aresult, it was possible to selectively remove the PMMA phase by adifference in etching rate between PS and PMMA, thereby allowing apattern 32 of PS to remain as shown in FIG. 3C. This PS pattern 32 wassubsequently employed as a mask material layer. More specifically, thisPS pattern 32 was transcribed onto the surface of the current diffusionlayer 15 by RIE using BCl₃ (23 sccm) and N₂ (7 sccm). This transcriptionwas performed for about 100 seconds under the conditions of: 0.2 Pa inpressure, and 500 W in power output. As a result, it was possible toform a finely recessed/projected pattern on the surface of the currentdiffusion layer 15 as shown in FIG. 3D. Alternatively, theaforementioned RIE may be performed by using BCl₃ (8 sccm), Cl₂ (5 sccm)and Ar (37 sccm) with other conditions being the same as describedabove. Thereafter, the remaining PS pattern was removed by an O₂ asherto obtain a structure as shown in FIG. 1.

In this embodiment, it was possible to uniformly form finelyrecessed/projected portions each projected portion having a cone-likeconfiguration on the exposed surface of the current diffusion layer 15,this exposed surface being functioning as a light-extracting surface.More specifically, the projected portion of the recessed/projectedportions was about 100±50 nm in base length, about 200±100 nm in heightand 20 to 40 degrees in apex angle. Due to the existence of these finelyrecessed/projected portions, it is now possible to take up light out ofthe current diffusion layer 15 even if the incidence angle at thelight-extracting surface is increased. Further, even if thelight-extracting surface is sealed with a transparent resin, it ispossible to improve the light extraction efficiency.

It was confirmed that the improvement of the light extraction efficiencywas dependent on the height of the projected portion in the finelyrecessed/projected portions. More specifically, it was found that whenthe height of the projected portion in the finely recessed/projectedportions was 100 nm (h=100 nm), the light extraction efficiency could beenhanced by a magnitude of about 1.3 times higher as compared with therewas no finely recessed/projected portions, and when the height of theprojected portion was 200 nm (h=200 nm), the light extraction efficiencycould be enhanced by a magnitude of about 1.5 times higher. Namely, itwas confirmed that the light extraction efficiency could besignificantly enhanced (enhancement by 10% or more) when the height ofthe projected portion was 100 nm or more. When the height “h” wasincreased over 200 nm, this enhancement was increased to 1.5 to 1.6times at most, and any further enhancement could not be obtained. It wasalso recognized that as long as the width “d” of the base of theprojected portion was confined within the range of 10 to 500 nm, it waspossible to expect a sufficient enhancement of the light extractionefficiency.

It was also found possible to obtain a sufficient enhancement of thelight extraction efficiency as long as at least 90% of the finelyrecessed/projected portions formed on the surface of the currentdiffusion layer 15 satisfied the aforementioned conditions. The creationof these finely recessed/projected portions would be possible only whenthe current diffusion layer 15 was subjected to the aforementionedtreatment, using the aforementioned diblock copolymer. Namely, it wouldbe impossible to obtain these finely recessed/projected portions by theconventional roughening work or etching work. It may be possible to formfinely recessed/projected portions having almost the same features asdescribed above by using a micro-lithographic technique such as EB, itwould lead to a prominent increase in manufacturing cost. Whereas, it isnow possible according to this embodiment to form these finelyrecessed/projected portions more cheaply and easily.

As for the diblock copolymer having a polymer chain which is capable ofexhibiting a sufficiently large difference in dry etching rate, it ispossible to employ a diblock copolymer having an aromaticring-containing polymer chain and an acrylic polymer chain. As for thearomatic ring-containing polymer chain, it is possible to employ apolymer chain which can be synthesized through the polymerization of atleast one monomer selected from the group consisting of vinylnaphthalene, styrene and derivatives thereof. As for the acrylic polymerchain, it is possible to employ a polymer chain which can be obtainedthrough the polymerization of at least one monomer selected from thegroup consisting of acrylic acid, methacrylic acid, crotonic acid, andderivatives thereof. A typical example of the diblock copolymer is a1:2.5 diblock copolymer comprising polystyrene and poly(methylmethacrylate), which was employed in this embodiment.

According to this embodiment, since the finely recessed/projectedportions can be uniformly created on the light-extracting surface, it isnow possible to prevent the degrading of the light extraction efficiencythat may be caused due to the influence by the total reflection oflight. As a result, it is now possible to enhance the light extractionefficiency and hence to enhance the luminance of LED. In contrast to theconventional surface-roughening treatment, of substrate usinghydrochloric acid, sulfuric acid, hydrogen peroxide or a mixed solutioncomprising these chemicals, the method of this embodiment enables toform finely recessed/projected portions in a very efficient mannerirrespective of the orientation of the crystal plane of substrate.

Moreover, due to the finely recessed/projected portions that have beenformed on the light-extracting surface, even the light that has beenre-absorbed by the activated layer due to the internal multi-reflectioncan be taken up out of the light-extracting surface, so that it is nowpossible to operate an LED at a relatively high temperature (up to 100°C. or more).

Second Embodiment

A PS pattern was formed by RIE under the same conditions as described inthe aforementioned first embodiment except that O₂ was substituted forCF₄.

In the same manner as described in the first embodiment, a polymer layer31 containing a diblock copolymer was formed on the surface of thecurrent diffusion layer 15 and then, the diblock copolymer was subjectedto phase separation. Then, the polymer layer 31 was subjected to etchingby RIE using O₂ gas (30 sccm) under the conditions of 13.3 Pa inpressure and 100 W in power output. In contrast with the etching usingCF₄, although it was impossible, in this case where O₂ was employed, toetch the polymer layer 31 down to the underlying substrate, it waspossible to relatively accurately remove the PMMA phase of the PS-PMMAblock, thereby forming a PS pattern.

This PS pattern was then transcribed onto the surface of the currentdiffusion layer 15 by RIE under the same conditions as described in theaforementioned first embodiment except that Cl₂ (5 to 40 sccm) wasemployed as an etching gas. Thereafter, the PS pattern left remained wasremoved by using an O₂ asher.

As a result, in the same manner as in the aforementioned firstembodiment, it was possible to form a pattern of recessed/projectedportions on the exposed surface of the current diffusion layer 15constituting a light-extracting surface with the projected portionthereof being about 100±50 nm in base length and about 200±100 nm inheight. Accordingly, it was possible to obtain almost the same effectsas those obtained in the first embodiment.

Third Embodiment

In this embodiment, a PS pattern was formed through the scission of themain chain of polymer by the irradiation of electron beam.

In the same manner as described in the first embodiment, a polymer layer31 containing a diblock copolymer was formed on the surface of thecurrent diffusion layer 15 and then, the diblock copolymer was subjectedto phase separation. Then, an electron beam was irradiated the entiresurface of the polymer layer 31 to cut the main chain of PMMA. On thisoccasion, the conditions of irradiating the electron beam were set to 2eV. Thereafter, the polymer layer 31 was subjected to development byusing a developing solution (for example, a mixed solution comprisingMIBK (methylisobutyl ketone) and IPA (isopropanol)). The resultantsurface of the polymer layer 31 was then rinsed by IPA or ethanol toselectively dissolve and remove the PMMA, thereby leaving a pattern 32of PS.

This PS pattern was then transcribed onto the surface of the currentdiffusion layer 15 by RIE under the same conditions as described in theaforementioned first embodiment except that Cl₂ (5 to 40 sccm) wasemployed as an etching gas. Thereafter, the PS pattern left remained wasremoved by using an O₂ asher.

As a result, in the same manner as in the aforementioned firstembodiment, it was possible to form a pattern of recessed/projectedportions on the exposed surface of the current diffusion layer 15constituting a light-extracting surface with the projected portionthereof being about 100±50 nm in base length and about 200±100 nm inheight. Accordingly, it was possible to obtain almost the same effectsas those obtained in the first embodiment.

Fourth Embodiment

In this embodiment, a material containing an aromatic ring-containingpolymer chain and an aliphatic double-bond polymer chain was employed asa diblock copolymer.

This aliphatic double-bond polymer is a polymer containing a double-bondin the main chain of the polymer, wherein the double-bond is cut off bythe effect of oxidation using ozone for instance. Therefore, it ispossible, in the case of a diblock copolymer containing an aromaticring-containing polymer chain and an aliphatic double-bond polymerchain, to selectively remove the aliphatic double-bond polymer chain. Asfor specific examples of the aliphatic double-bond polymer chain, it ispossible to employ polydiene-based polymer and derivatives thereof. Asfor specific examples of the diblock copolymer containing an aromaticring-containing polymer chain and an aliphatic double-bond polymerchain, it is possible to employ a diblock copolymer comprisingpolystyrene and polybutadiene, a diblock copolymer comprisingpolystyrene and polyisoprene, etc.

In this embodiment, a 1:2.5 diblock copolymer comprising polystyrene(PS)-polyisoprene was employed to form a polymer layer on the currentdiffusion layer 15 in the same manner as described in the firstembodiment, and then, the diblock copolymer was subjected to phaseseparation. Subsequently, this phase-separated diblock copolymer wasleft to stand in an ozone atmosphere for 5 minutes, thereby removing thepolyisoprene, thus forming a pattern of PS. Thereafter, by the sameprocedures as described in the aforementioned first embodiment, thepattern of PS was transcribed onto the surface of the current diffusionlayer 15.

As a result, it was possible to form a pattern of recessed/projectedportions on the exposed surface of the current diffusion layer 15constituting a light-extracting surface with the projected portionthereof being about 100±50 nm in base length and about 200±100 nm inheight. Accordingly, it was possible to obtain almost the same effectsas those obtained in the first embodiment. Even when a copolymercomprising polystyrene and polybutadiene was employed as a diblockcopolymer, it was possible, through the same process as described above,to form recessed/projected portions having almost the same features asdescribed above.

Fifth Embodiment

FIGS. 4A to 4D are cross-sectional views each illustrating, stepwise,the manufacturing steps of an LED according to a fifth embodiment of thepresent invention. Incidentally, the same portions as those of FIGS. 3Ato 3D will be identified by the same reference numbers in FIGS. 4A to4D, thereby omitting the detailed explanation thereof.

In this embodiment, the finely recessed/projected portions were formedon the surface of a transparent layer formed on the current diffusionlayer.

First of all, after a laminate having the same structure as that of FIG.3A was formed, a transparent film 41 was formed on the surface of thecurrent diffusion layer 15. This transparent film 41 can be formed, forexample, by a sputtering method, a CVD method or a coating method bySiO₂, SiN₂, TiO₂, etc.

Then, by using a solution of the same copolymer and by the sameprocedures as employed in the aforementioned first embodiment, a polymerfilm 31 was formed on the transparent film 41. Thereafter, the polymerfilm 31 was subjected to annealing in a nitrogen atmosphere at atemperature of 210° C. for 4 hours to permit the diblock copolymer totake place the phase separation thereof.

The polymer layer containing this phase-separated diblock copolymer wasthen subjected to etching by RIE to form a pattern 32 of PS, which wassubsequently transcribed onto the surface of the transparent film 41 asshown in FIG. 4C. The RIE in this case can be performed using an etchinggas such as CF₄, CHF₃, C₄F₈, SF₆, etc. and under the conditions of: 5-10Pa in pressure, and 100-1000 W in power output.

Thereafter, the PS pattern remaining was removed by using an O₂ asher toform finely recessed/projected portions on the surface of thetransparent film 41 as shown in FIG. 4D. These finely recessed/projectedportions were found excellent in uniformity as those of the firstembodiment with the projected portion thereof being about 100±50 nm inbase length, about 200±100 nm in height.

Alternatively, the finely recessed/projected portions formed in thetransparent film 41 may be transcribed onto the current diffusion layer15 subsequent to the formation of the structure shown in FIG. 4D, andthen, the transparent film 41 may be removed by a chemical solution suchas HF, NH₄F, etc. In this case, the finely recessed/projected portionscan be formed on the surface of the current diffusion layer 15 in thesame manner as described in the first embodiment.

As explained above, according to this embodiment, since finelyrecessed/projected portions can be uniformly formed on the surface ofthe transparent film 41 or the current diffusion layer 15, bothfunctioning as a light-extracting surface, it is possible to prevent thedegrading of light extraction efficiency that may be otherwise caused tooccur due to the influence of the total reflection of light.Accordingly, it was possible to obtain almost the same effects as thoseobtained in the first embodiment.

Sixth Embodiment

FIGS. 5A and 5B are cross-sectional views each illustrating the elementstructure of an LED according to a sixth embodiment of the presentinvention.

The LED shown in FIG. 5A is a Junction Up type LED where the light isextracted from a surface located opposite to the substrate 50. In thiscase, an n-type GaN buffering layer 51, an n-type GaN clad layer 52, anMQW activated layer 53 containing InGaN/GaN, a p-type AlGaN cap layer54, and a p-type GaN contact layer 55 are successively deposited on thesurface of an n-type GaN substrate 50. A p-side electrode 57 is formedon part of the surface of the contact layer 55 with the remainingportion of the surface of the contact layer 55 being left exposed. Onthe other hand, an n-side electrode 58 is formed on the bottom surfaceof the substrate 50. Finely recessed/projected portions 55 a are formedon the exposed surface of the contact layer 55 by the same procedures asexplained above. Alternatively, the finely recessed/projected portionsmay be formed in the dielectric film which is disposed on the exposedsurface of the contact layer 55.

Since these finely recessed/projected portions 55 a can be uniformlyformed on the surface of the light-extracting surface, it is possible toenhance the light extraction efficiency.

The LED shown in FIG. 5B is a Junction Down type LED where the light isextracted from the substrate 50 side. In this case also, the same kindsof layers as those of FIG. 5A, i.e. the layers 51, 52, 53, 54 and 55 aresuccessively deposited on the surface of an n-type GaP substrate 50. Ap-side electrode 57 is formed on the surface of the contact layer 55,and an n-side electrode 58 which has been patterned is formed partiallyon the bottom surface of the substrate 50. The remaining region of thebottom surface of the substrate 50 is left exposed and provided withfinely recessed/projected portions 50 a which have been formed by thesame procedures as explained above.

Since these finely recessed/projected portions 50 a can be uniformlyformed on the bottom surface of the substrate 50 functioning as alight-extracting surface, it is possible to enhance the light extractionefficiency.

In the case of the LED shown in FIG. 5B, the light emitted from the MQWactivated layer 53 is reflected by each of the end faces, thus enablingthe light to be extracted from the finely recessed/projected portions 50a which are formed on the top surface of the substrate, thereby makingit possible to minimize the density of light at the sidewall of chip. Asa result, it is possible to prevent the degrading of the resin locatedon the sidewall of chip and hence to prevent the discoloration of theresin even if the LED is actuated for a long period of time.

Seventh Embodiment

FIGS. 6A and 6B are cross-sectional views each illustrating the elementstructure of an LED according to a seventh embodiment of the presentinvention.

The LED shown in FIG. 6A is a Junction Up type LED where the light isextracted from a surface located opposite to the substrate 60. In thiscase, an AlGaN buffering layer 61, an n-type GaN contact layer 62, anMQW activated layer 63 containing InGaN/GaN, a p-type AlGaN cap layer64, a p-type GaN contact layer 65 and a transparent electrode 66 made ofITO for instance are successively deposited on the top surface of asapphire substrate 60. This laminate is partially etched in such amanner that the etched region is extended from the transparent electrode66 down to an intermediate portion of the n-type GaN contact layer 62.

A p-side electrode 67 is formed on part of the surface of thetransparent electrode 66 with the remaining portion of the surface ofthe transparent electrode 66 being left exposed. On the exposed surfaceof the contact layer 62, there is formed an n-side electrode 68. Finelyrecessed/projected portions 66 a are formed on the exposed surface ofthe transparent electrode 66 by using the same procedures as explainedabove.

Since these finely recessed/projected portions 66 a can be uniformlyformed on the surface of the transparent electrode 66 constituting alight-extracting surface, it is possible to enhance the light extractionefficiency.

The LED shown in FIG. 6B is a Junction Down type LED where the light isextracted from the substrate 60 side. In this case also, the same kindsof layers as those of FIG. 6A, i.e. the layers 61, 62, 63, 64 and 65 aresuccessively deposited on the surface of a sapphire substrate 60. Thislaminate is partially etched in such a manner that the etched region isextended from the p-type contact layer 65 up to an intermediate portionof the n-type contact layer 62. A p-side electrode 67 is formed on thesurface of the p-type contact layer 65, and an n-side electrode 68 isformed on the exposed surface of the n-type contact layer 62. Finelyrecessed/projected portions 60 a are formed the entire surface of thesubstrate 60 by using the same procedures as explained above.

Since these finely recessed/projected portions 60 a can be uniformlyformed on the bottom surface of the substrate 60 functioning as alight-extracting surface, it is possible to enhance the light extractionefficiency.

Eighth Embodiment

FIG. 7 is a cross-sectional view illustrating the element structure ofan LED according to an eighth embodiment of the present invention.

In this LED shown in FIG. 7, a p-type GaP buffering layer 71, a p-typeInGaP adhesion layer 72, a p-type InAlP clad layer 73, an InGaAlPactivated layer 74, an n-type InAlP clad layer 75 and an n-type InGaAlPcurrent diffusion layer 76 are successively deposited on the surface ofa p-type GaP substrate 70.

At the central region of the surface of the current diffusion layer 76is formed a laminate containing an n-type GaAs contact layer 77, ani-type InAlP block layer 78, an i-type GaAs block cover layer 79 and ann-side electrode 81. On the peripheral region of the surface of thecurrent diffusion layer 76, there are deposited the n-type GaAs contactlayer 77 and the n-side electrode 81. On the other hand, a p-sideelectrode 82 which has been patterned is formed on the bottom surface ofthe substrate 70. Finely recessed/projected portions 83 are formed onthe exposed surface of the current diffusion layer 75 by the sameprocedures as explained above.

Next, the process of manufacturing the LED according to this embodimentwill be explained with reference to FIGS. 8A to 8C.

First of all, as shown in FIG. 8A, an n-type GaAs buffering layer 91(0.5 μm in thickness; 4×10¹⁷ cm⁻³ in carrier concentration), an i-typeInGaP etch-stop layer 92 (0.2 μm), an i-type GaAs block cover layer 79(0.1 μm), an i-type InAlP block layer 78 (0.2 μm), an n-type GaAscontact layer 77 (0.1 μm in thickness; 1×10¹⁸ cm⁻³ in carrierconcentration), an n-type InGaAlP current diffusion layer 76 (1.5 μm inthickness; 4×10¹⁷ cm⁻³ in carrier concentration), an n-type InAlP cladlayer 75 (0.6 μm in thickness; 4×10¹⁷ cm⁻³ in carrier concentration), anInGaAlP-MQW activated layer 74 (0.72 μm in thickness; 621 nm inwavelength), a p-type InAlP clad layer 73 (1 μm in thickness; 4×10¹⁷cm⁻³ in carrier concentration), a p-type InGaP adhesion layer 72 (0.05μm in thickness; 3×10¹⁸ cm⁻³ in carrier concentration), and an n-typeInAlP cap layer 95 (0.15 μm in thickness; 2×10¹⁵ cm⁻³ in carrierconcentration) were successively formed on the top surface of the n-typeGaAs substrate 90.

Then, the cap layer 95 was removed to expose the adhesion layer 72. Onthe other hand, a p-type GaP layer 71 (0.2 μm in thickness; 3×10¹⁸ cm⁻³in carrier concentration) was allowed to grow on the surface of a p-typeGaP substrate 70 having a thickness of 150 μm to prepare a supportingsubstrate. Then, this supporting substrate was adhered onto the adhesionlayer 72. Thereafter, the GaAs substrate 90, the buffering layer 91 andthe etch-stop layer 92 were etched away to obtain a structure as shownin FIG. 8B.

Then, as shown in FIG. 8C, the block cover layer 79, the block layer 78and the contact layer 77 were etched so as to form a pattern ofelectrode. On this occasion, the central portion of these layers waspatterned into a circular configuration, and the peripheral portionthereof was formed into a pattern of fine linear configuration, and atthe same time, the block cover layer 79 and the block layer 78 wereremoved. In either of patterns, an n-side electrode 81 was formed on theuppermost layer thereof, while a p-side electrode 82 was formed on thebottom surface of the substrate 70. Although not clearly shown in thedrawings, the p-side electrode 82 was formed as a circular pattern atfour locations of the substrate excluding the central region of thesubstrate in order to enhance the light extraction efficiency of theregion immediately below the portion where the n-side electrode 81 wasnot located. This p-side electrode 82 can be formed all over the bottomsurface of the substrate 70.

Thereafter, finely recessed/projected portions were formed on thesurface of the current diffusion layer 76 by using a diblock copolymerand by using the same procedures as explained above, thereby obtaining astructure as shown in FIG. 7.

Since these finely recessed/projected portions 83 can be uniformlyformed the entire surface of the current diffusion layer 76 functioningas a light-extracting surface except the region where the electrode 81was formed, it is possible to enhance the light extraction efficiency.

Ninth Embodiment

A method of working an underlying film by using an oxide film (such asSiO₂) or a nitride film (such as SiN) as a mask will be explained withreference to FIGS. 9A to 9C.

First of all, as shown in FIG. 9A, an SOG film 93 having a thickness of0.1 μm and comprising an SiO₂ film was formed on the surface of theInGaAlP current diffusion layer 76 of the laminate structure shown inFIG. 7 by a spin-coating method. Then, a polymer film containing adiblock copolymer was formed on the surface of the SOG film 93 in thesame manner as described in the first embodiment, and the polymer layerwas allowed to take place the phase separation thereof. Thereafter, thisphase-separated polymer film was subjected to etching for 30 seconds byRIE using O₂ gas (30 sccm) under the conditions of 13 Pa in pressure and100 W in power output, thereby forming a polymer pattern 94.

This polymer pattern 94 was then employed as a mask to etch the SOG film93 for about 100 seconds by RIE using CF₄ gas (30 sccm) under theconditions of 1.3 Pa in pressure and 100 W in power output, therebyforming a pattern of SOG as shown in FIG. 9B.

Then, the resultant surface was subjected to etching for about 100seconds by RIE using BCl₃ (8 sccm), Cl₂ (5 sccm) and Ar (37 sccm) underthe conditions of: 0.2 Pa in pressure, and 500 W in power output. As aresult, it was possible, as shown in FIG. 9C, to form finelyrecessed/projected portions 83 with the projected portion having aminute cone-like configuration 50-300 nm in width and 100-500 nm inheight on the surface of the InGaAlP current diffusion layer 76. In thiscase, the SOG (oxide film) 93 may be left at the apex portion of thefinely recessed/projected portions, i.e. no trouble would be raised evenif the SOG is left in this manner.

It was possible in this manner to uniformly form finelyrecessed/projected portions on the surface of the InGaAlP currentdiffusion layer 76, each projected portion having a cone-likeconfiguration about 100±50 nm in base length and about 200±100 nm inheight. FIG. 10 shows an electron microphotograph of the finelyrecessed/projected portions.

Tenth Embodiment

A method of working an underlying substrate by using a multi-layerresist system will be explained with reference to FIGS. 11A to 11C.

First of all, as shown in FIG. 11A, an underlying resist film (positivenovolac resist) 95 having a thickness of 0.1 μm was formed on thesurface of the InGaAlP current diffusion layer 76. The resist to beemployed in this case may not contain a photosensitive agent. Then, anSOG film 93 and a polymer film were formed on the surface of theunderlying resist film 95 in the same manner as described above. Afterthe diblock copolymer contained in the polymer layer was allowed tounderego phase separation thereof, this phase-separated polymer film wassubjected to etching for 30 seconds by RIE using O₂ gas (30 sccm) underthe conditions of 13 Pa in pressure and 100 W in power output, therebyforming a polymer pattern 94.

This polymer pattern 94 was then employed as a mask to etch the SOG film93 by RIE, and the underlying resist film 95 was etched by RIE using O₂gas (8 sccm) and N₂ gas (80 sccm) under the conditions of 2 Pa inpressure and 300 W in power output, thereby forming a resist pattern 95a as shown in FIG. 11B.

Then, after the InGaAlP current diffusion layer 76 was etched by RIEunder the same conditions as described in the ninth embodiment, a resistpattern 95 a was peeled off by using an O₂ asher, thereby forming, asshown in FIG. 1C, finely recessed/projected portions 83 on the surfaceof the InGaAlP current diffusion layer 76, each projected portionthereof having a cone-like configuration about 50-200 nm in width and100-500 nm in height.

It was possible in this manner to uniformly form finelyrecessed/projected portions on the surface of the InGaAlP currentdiffusion layer 76, each projected portion having a cone-likeconfiguration 100±50 nm in base length and 300±150 nm in height.

According to this embodiment, since the finely recessed/projectedportions that have been defined as mentioned above are formed on thelight-extracting surface, it is now possible to prevent the degrading ofthe light extraction efficiency that may be caused due to the influenceby the total reflection of light. As a result, it is now possible toenhance the light extraction efficiency. Furthermore, it is now possibleto minimize the internal absorption loss that may be caused by themulti-reflection in the interior of the semiconductor layer, therebymaking it possible to realize a light-emitting element capable ofextremely minimizing temperature increase. Additionally, since thesurface-roughening treatment using a diblock copolymer is applied to thelight-extracting surface, it is now possible to uniformly form finelyrecessed/projected portions without depending on the crystal orientationof the underlying layer.

The present invention should not be construed as being limited to theaforementioned embodiments. For example, as for the materials forforming the polymer layer, it is possible to employ any diblockcopolymer as long as they are capable of selectively removing one of thecomponents that have been phase-separated. The finely recessed/projectedportions can be formed on any desired layer as long as it is located atan uppermost layer of the light-extracting side and at the same time,capable of being worked through etching using a phase-separated polymerfilm as a mask.

Further, as far as the projected portion of the finelyrecessed/projected portions is formed of a cone-like configuration, itis possible to obtain the advantages as mentioned above. Furthermore,the finely recessed/projected portions having a cone-like configurationmay be formed on each of the surfaces (top and side surfaces) of thechip other than the portions where electrodes are formed. Theaforementioned advantages would not be hindered even if the electrodesare formed after the finely recessed/projected portions have been formedall over the light-extracting surface. The present invention can beexecuted by modifying it in various ways as long as such variations donot exceed the subject matter of the present invention.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A semiconductor light-emitting element comprising: a substrate havinga first surface and a second surface; and a semiconductor laminateformed on said first surface of said substrate and containing alight-emitting layer; wherein said light-emitting element is providedwith a light-extracting surface which is constituted by a finelyrecessed/projected surface, at least 90% of which is constructed suchthat the height of the projected portion thereof having a cone-likeconfiguration is 100 nm or more, and the width of the base of theprojected portion is within the range of 10-500 nm.
 2. The semiconductorlight-emitting element according to claim 1, wherein saidlight-extracting surface is constituted by said second surface ofsubstrate.
 3. The semiconductor light-emitting element according toclaim 2, wherein said substrate is formed of a transparent substrate. 4.The semiconductor light-emitting element according to claim 1, whereinsaid light-extracting surface is constituted by an outermost surface ofsaid semiconductor laminate.
 5. The semiconductor light-emitting elementaccording to claim 1, wherein at least one of said projected portions isformed of a cone-shaped configuration having an apex angle ranging from20 to 80 degrees.
 6. The semiconductor light-emitting element accordingto claim 1, wherein at least one of said projected portions is provided,at the apex thereof, with a very small transparent portion constitutedby a material which differs in kind from the material of saidlight-extracting surface.
 7. The semiconductor light-emitting elementaccording to claim 1, wherein at least one of said projected portions isprovided with a flat apex.
 8. The semiconductor light-emitting elementaccording to claim 1, wherein at least one of said projected portions isprovided with a flat apex, on which a very small transparent portion isdisposed, said very small transparent portion being formed of a materialdiffering in kind from the material of said light-extracting surface. 9.The semiconductor light-emitting element according to claim 2, whereinsaid substrate is provided, on said second surface, with a transparentoxide film or a transparent nitride film, and said finelyrecessed/projected portions are constituted by a surface of saidtransparent oxide film or of said transparent nitride film.
 10. Thesemiconductor light-emitting element according to claim 4, wherein saidsemiconductor laminate comprises a current diffusion layer is disposedat the uppermost layer of said semiconductor laminate, and said finelyrecessed/projected portions exists on an exposed surface of said currentdiffusion layer.
 11. The semiconductor light-emitting element accordingto claim 10, wherein said current diffusion layer is provided, on theexposed surface thereof, with a transparent oxide film or a transparentnitride film, and said finely recessed/projected portions are formed ona surface of said transparent oxide film or of said transparent nitridefilm. 12-23. (canceled)